Как искать строку в строке?

line_shortfile in line_longfile

>>> line_shortfile = 'water'
>>> line_longfile = 'water2'
>>> 
>>> line_shortfile in line_longfile
True
>>>

>>> 'aaaa' in 'bba'
False
>>> 'aaaa' in 'aab'
False
>>> 'aaaa' in 'aaaab'
True
>>> 'hot water' in 'hot water'
True

myFile = open('/home/user/test/out.txt', 'w')
with open('/home/user/test/list_test.txt', 'r') as longfile:
    for line_longfile in longfile:
        with open('/home/user/test/dict_sort.txt', 'r') as shortfile:
            for line_shortfile in shortfile:
                if line_shortfile in line_longfile:
                    myFile.write(line_longfile)
                    print line_longfile
                    break
myFile.close()

file1 = open('2.txt').readlines()
file2 = open('1.txt').readlines()
for i in file1:
    for j in file2:
        if i in j:
            print(i, j)

file1 = open('1.txt').readlines()
file2 = open('2.txt').readlines()
for i in file1:
    for j in file2:
        if i in j:
            print(i, j)

'water\n'

'water2\n'

myFile = open('/home/user/test/out.txt', 'w')
with open('/home/user/test/list_test.txt', 'r') as longfile:
    for line_longfile in longfile:
        with open('/home/user/test/dict_sort.txt', 'r') as shortfile:
            for line_shortfile in shortfile:
                print line_longfile.find(line_shortfile)
                if not line_longfile.find(line_shortfile) < 0:
#                if line_shortfile in line_longfile:
                    myFile.write(line_longfile)
                    print line_longfile
                    break
myFile.close()

.rstrip('\n')